Anionic fluorinated surfactants are commonly used in the emulsion polymerization of fluorinated monomers to produce fluoropolymers. The resulting fluoropolymer dispersions may be coagulated so as to recover the fluoropolymer therefrom and sell the fluoropolymer in its solid form or the fluoropolymer dispersions can be, optionally after upconcentration, be sold as such. The fluorinated surfactants used are generally expensive. Furthermore, frequently used anionic fluorinated surfactants are perfluoroalkanoic acids and salts thereof. These surfactants may be environmentally undesirable in aqueous dispersions and/or waste water streams. Hence, it is desirable to recover the fluorinated surfactants from the dispersions and waste water streams.
Anion exchange resins have been used in the art to recover fluorinated surfactants from waste water streams generated during the manufacturing of fluoropolymers as well as to recover fluorinated surfactants from fluoropolymer dispersions. For example, WO 00/35971 describes the use of an anion exchange resin to recover a fluorinated surfactant from a fluoropolymer dispersion. WO 99/62830 and WO 99/62858 describe the use of an anion exchange resin to recover fluorinated surfactants from waste water streams.
Strongly basic anion exchange resins, which typically have quaternary ammonium groups, are known to be the most effective in the recovery of fluorinated surfactants. Unfortunately, it has also been found difficult to elute and thus recover the fluorinated surfactant from a strong basic anion exchange resin. U.S. Pat. No. 6,642,415 discloses that the elution with solutions of 1 mol/liter each of NH3, NaOH and KF of a strongly basic anion exchanger resin that is charged to breakdown with the ammonium perfluorooctanoic acid (APFOA) yields APFOA concentrations in the range of only 0.1 mmol/liter (40 ppm) in the eluate. Consequently, such method for recovering APFOA from larger volumes of aqueous effluent is not economically feasible. U.S. Pat. No. 6,642,415 recommends the use of a weakly or moderately strong anion exchange resin and to elute such resin with an ammonia containing organic solvent optionally in the presence of alkali hydroxides.
U.S. Pat. No. 3,882,153 discloses the use of an aqueous NH3 solution for the recovery of an anionic fluorinated surfactant loaded on a weakly basic anion exchange resin. It is demonstrated in the examples of this US patent that while an elution with an aqueous ammonia solution is highly effective for eluting a weakly basic anion exchange resin, the process is ineffective for eluting a strongly basic anion exchange resin.
EP 14431 discloses a method in which the fluorinated surfactant is recovered from basic anion exchange resins using a solution of a mineral acid in an organic solvent. However, only about 70% of the fluorinated surfactant is recovered from a strongly basic anion exchange resin. Further in the method of the EP application, the surfactant is converted into its methyl ester during the recovery.